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Researchers found that people who were better able to put off receiving a reward at age 4 had lower body mass indexes (BMIs) three decades later, when the researchers followed up with them. For every minute that children resisted the temptation to eat a marshmallow placed in front of them, their BMIs decreased by an average 0.2 points in adulthood.

BMI is a measure of body fatness. People with BMIs between 18 and 24 are considered to be normal weight, while a BMI higher than 25 indicates being overweight, and over 30 indicates obesity.

"In today's world, there's so much unhealthy food everywhere," said lead researcher Tanya Schlam of the University of Wisconsin School of Medicine and Public Health. Understanding the limitations of people's abilities to control themselves may lead to viable means of treating obesity, Schlam said.

The study was published in the Aug. 16 edition of the Journal of Pediatrics.

Sweet treats and 4-year-olds

In the original "marshmallow experiment," Stanford University researchers studied 653 children between 1968 and 1974. The 4-year-olds were presented with a marshmallow and told that if they did not eat the marshmallow for an unspecified amount of time (which was ultimately 15 minutes), they would get two marshmallows.

Over the subsequent decades, researchers followed up with the study's original participants and found correlations between their abilities to wait as children and various aspects of their adolescent and adult lives.

"Academics and social interactions just went better for kids who were more able to delay gratification," Schlam said.

In the new study, Schlam and her colleagues looked at the BMIs of 164 of the participants.

The link they found between the 4-year-olds' wait times and their adult BMIs suggests that the effect is particularly strong, she said, but she also noted that the obesity rate among study participants was much lower than the U.S. national average — 9 percent versus 34 percent.

Preventing obesity

Because of the widespread availability of unhealthy foods today, teaching children to delay gratification when they are young could help their abilities to make healthy choices later in life, Schlam said.

The part of the brain associated with self-control is the prefrontal lobe, which doesn't fully develop until age 25, which suggests that self-control can be learned during childhood and into adulthood, she said.

Laura Martin, a preventative medicine professor at the University of Kansas Medical Center, said that incorporating lessons on how to delay gratification into health education curriculum could help.

People who have trouble delaying gratification are also more likely to become addicted to drugs, Martin said.

Schlam said that even people with strong willpower often benefit from simply decreasing the availability of unhealthy foods around them, because self-control goes only so far.

"People have self-control, but it's a limited resource. It's much better to create a society where we don’t have to exercise such a self- control," she said, pointing to New York Mayor Michael Bloomberg's proposal to limit the size of sodas as an example of removing the decision from the individual.

"We're talking about half of the population being overweight," she said. It's not enough to say, 'People, just control yourselves.'"